1. Field of the Invention
The present invention relates to a mobile communication system and, more particularly, to an uplink synchronization detecting method of the mobile communication system.
2. Background of the Related Art
In a general mobile communication system, a base station checks a synchronization state of uplink radio link sets of each frame. The base station includes a multi-path searcher and a plurality of fingers. The multi-path searcher continuously searches the strength of receiving signals of uplink paths and allocates a path with a greatest path to the finger. Then, the finger receives a component that reaches the base station through the allocated path.
The general uplink physical channel includes a dedicated physical channel (DPCH) which includes, as shown in FIG. 1, a dedicated physical control channel (DPCCH) and a dedicated physical data channel (DPDCH). The dedicated physical control channel includes a pilot field for a pilot pattern, a TPC (Transmit Power Control command) field for controlling a transmission power of a mobile terminal, a TFCI (Transmit Format Combination Indicator) field and an FBI (FeedBack Information) for information to be fed back from the mobile terminal to the base station. The dedicated physical control channel includes a data of a higher layer.
There are various methods for detecting uplink synchronization, including, for example, the following three methods. In a first method, a synchronization detection is performed on the basis of a CRC (Cyclic Redundancy Check) of an uplink receiving data received through the DPDCH. In a second method, a synchronization detection is performed on the basis of a quality of the DPCCH. In a third method, a synchronization detection is performed on the basis of an uplink receiving SIR (Signal to Interference Ratio).
When the synchronization detection is performed on the basis of the CRC of the uplink receiving data, if no CRC error is generated, it is judged to be in an in-synchronization status. When the synchronization detection is performed on the basis of the quality of the uplink DPCCH or when the synchronization detection is performed on the basis of the uplink receiving SIR, if a DPCCH quality for a certain time period (N frames) or a receiving SIR is greater than a synchronization threshold value, it is judged to be in the in-synchronization status.
When the DPCCH quality or when the uplink receiving SIR is measured for a certain time period (N frames) for judging an uplink synchronization, at least N frames are taken for detecting synchronization. And, in order to heighten a reliability of the synchronization detection, the measurement time (N frames) needs to be increased.
In the uplink, an initial transmit power of a mobile terminal becomes very high due to an error of an open-loop power control or because of out-of synchronization due to a temporary deep fading. Accordingly, uplink interference is increased due to the high transmit power of the mobile terminal, resulting in longer times for synchronization detection. In addition, if the high transmit power of the mobile terminal cannot be quickly controlled to a suitable low level due to the longer time used for synchronization detection, the system becomes unstable and uplink capacity is reduced.
Alternatively, in the case that the uplink synchronization detection is performed on the basis of the CRC of the uplink receiving data, a probability of the problem described above can be reduced. However, if the transmit power of the mobile terminal is low, a block error rate is greatly increased and reduces a synchronization detection probability, thereby causing a problem in that significant time is required for uplink synchronization detection.
Moreover, in the case of the uplink, it happens that only the DPCCH is maintained without the DPCDCH, making it difficult to judge an uplink synchronization detection by using only the CRC of the uplink receiving data. The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.